1. Field of the Invention
The invention relates to an organic electroluminescent device (hereinafter, also referred to as “organic EL device”, “luminescent device” or “EL device”) that emits a light by converting an electric energy into a light.
2. Description of the Related Art
Research and development of various display devices have become active today, and among these, organic electroluminescent devices (EL devices) have been focused as promising devices among various devices since the EL device is able to emit a quite bright light at a low voltage.
The organic electroluminescent device is composed of an electroluminescent layer or a pair of counter electrodes interposed with a luminescent layer or a plurality of organic layers including the luminescent layer. The organic electroluminescent device uses light emission from excitons generated by recombination of electrons injected from a cathode and holes injected from an anode in the luminescent layer, or uses light emission from excitons of other molecules generated by energy transfer from the excitons.
Characteristics required for the organic electroluminescent device include high luminous efficiency, low driving voltage and high durability (long service life).
With respect to high luminous efficiency and long service life, a technology for providing an electron-transporting control layer for suppressing electrons from flowing into the luminescent layer has been disclosed (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2004-273163).
In another art, luminous efficiency is improved by preventing the holes from leaking by providing a hole blocking layer (see, for example, JP-A Nos. 2000-243571 and 2000-3790).
However, luminous efficiency, driving voltage and durability cannot be considered to be sufficient in any of the organic electroluminescent devices disclosed in the above-mentioned patent publications, and further improvements of the characteristics are required.